This invention relates to sustained release tablets, and particularly to such tablets comprised of a fine particle sized hydrophilic polymeric composition.
Polymeric compositions have been widely used as a matrix base for compressed tablets. Such tablets typically contain a medicament or a vitamin whose rate of release into the system is delayed or controlled by the matrix base. Controlled release tablets are desirable because they provide a method of delivering a long-lasting dose in a single application without overdosing the system.
Typically, an effective amount of the polymeric matrix composition is employed. It is desirable to employ as little amount of polymeric composition as possible to provide the intended release profile, to obtain minimum dosage size or to obtain good compression properties. For such applications, a highly hydrophilic polymeric composition is suitably employed. Such a composition rapidly hydrates and forms a gel-like layer in the tablet through which the dosage composition is released to the system. An example of a preferred hydrophilic polymeric composition is a cellulose ether sold as METHOCEL.RTM. K4M and K15M by The Dow Chemical Company, which has a hydroxypropoxyl substitution of between about 4 to about 12 weight percent, and a methoxyl substitution of between about 19 to about 25 weight percent.
In U.S. Pat. No. 4,369,172 it is disclosed that hydroxypropyl methylcellulose ethers having a hydroxypropoxyl content of from 9 to 12 percent and a number average molecular weight of less than about 50,000 provides the best sustained release. Moreover, the effect of hydration and gel formation is de-emphasized in favor of the chemical composition of the hydroxypropyl methylcellulose.
Cellulose ethers, such as METHOCEL.RTM. K, are desirable polymeric matrix compositions because they are derived from naturally occurring cellulose, and are free-flowing, readily compressible powders. Unfortunately, not all cellulose ethers hydrate rapidly, and therefore do not provide a desirable release profile for compressed tablets.
Yet another factor affecting the performance of the tablet is the chemical characteristics of the drug employed. Certain polymers can be employed beneficially for some drugs, but not for others. The degree of water-solubility of the drug, the drug's molecular weight and the diffusion coefficient in a hydrated polymer gel layer can be critical.
It would be desirable to have additional cellulose ether polymeric matrix materials which would provide sufficient release profiles for compressed tablets.